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WebGPURenderer: Optimize VSM shadow code #32209

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Nov 7, 2025
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WebGPURenderer: Optimize VSM shadow code #32209

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27 changes: 17 additions & 10 deletions src/nodes/lighting/ShadowFilterNode.js
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Original file line number Diff line number Diff line change
Expand Up @@ -185,8 +185,6 @@ export const PCFSoftShadowFilter = /*@__PURE__*/ Fn( ( { depthTexture, shadowCoo
*/
export const VSMShadowFilter = /*@__PURE__*/ Fn( ( { depthTexture, shadowCoord, depthLayer } ) => {

const occlusion = float( 1 ).toVar();

let distribution = texture( depthTexture ).sample( shadowCoord.xy );

if ( depthTexture.isArrayTexture ) {
Expand All @@ -197,19 +195,28 @@ export const VSMShadowFilter = /*@__PURE__*/ Fn( ( { depthTexture, shadowCoord,

distribution = distribution.rg;

const hardShadow = step( shadowCoord.z, distribution.x );
const mean = distribution.x;
const variance = max( 0.0000001, distribution.y.mul( distribution.y ) );

const hardShadow = step( shadowCoord.z, mean );

If( hardShadow.notEqual( float( 1.0 ) ), () => {
// Early return if fully lit
If( hardShadow.equal( 1.0 ), () => {

const distance = shadowCoord.z.sub( distribution.x );
const variance = max( 0, distribution.y.mul( distribution.y ) );
let softnessProbability = variance.div( variance.add( distance.mul( distance ) ) ); // Chebeyshevs inequality
softnessProbability = clamp( sub( softnessProbability, 0.3 ).div( 0.95 - 0.3 ) );
occlusion.assign( clamp( max( hardShadow, softnessProbability ) ) );
return float( 1.0 );
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@Mugen87 Mugen87 Nov 7, 2025 •
edited
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This line triggers a new warning in the VSM demo webgpu_shadowmap_vsm:

THREE.TSL: Return statement used in an inline 'Fn()'. Define a layout struct to allow return values.

/cc @sunag


} );

return occlusion;
// Distance from mean
const d = shadowCoord.z.sub( mean );

// Chebyshev's inequality for upper bound on probability
let p_max = variance.div( variance.add( d.mul( d ) ) );

// Reduce light bleeding by remapping [amount, 1] to [0, 1]
p_max = clamp( sub( p_max, 0.3 ).div( 0.65 ) );

return max( hardShadow, p_max );

} );

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